1. Field
The following inventions disclosure is generally concerned with optical devices and sensors and specifically concerned with optical condensing devices and sensor systems suitable for use in conjunction with non-invasive biometric measurements.
2. Prior Art
Electronic heart rate monitors are sometimes used by athletes, persons practicing vigorous exercise, and advanced health practitioners, to monitor the state of their heart during various conditions. It is desirable to dynamically display heart rate information in an easily accessible location. The face of a wristwatch provides such a convenient location because a wristwatch may be comfortably worn during exercise and can be easily viewed without distraction or other interruption of the exercise.
Thus, combining a heart rate monitor with a wristwatch has long been a goal of designers of advanced bio-instrumentation systems. Indeed, many systems have been developed with the intent of reaching such goal. These systems may be classified in three general classes. A first class includes a wristwatch in communication with a remote sensor/detector which is coupled to tissue. Generally, a chest strap having a sensor thereon in close proximity to the heart where a strong signal is easily detected, communicates via radio with the wristwatch where a digital numeric display indicates heart rate or other biometric information. While this arrangement has the advantage of reliable detection, it is not convenient to use the chest strap which is distracting and uncomfortable to wear. In addition, these apparatus tend to be awkward to deploy and thus lack the utility desired by consumers of these devices.
Competing systems have the entire detector/sensor, computer and display all integrated into the same, single unit. Some of these versions provide two metallic electrodes at the watch face which are touched simultaneously with two fingers of the opposite hand. The fingers are placed in electrical contact with the metallic electrodes whereby electrical impulses within the body can be sensed and translated to a pulse rate measurement. A computer within the watch case determines the heart rate and presents that information at a graphical user interface such as an LED display. These types of devices are included in a second class of wristwatch heart rate monitors. While these devices can quite accurately measure heart rate, they suffer from the inconvenience which arises from the need to apply two fingers from one hand at the wrist of the other. Additionally, holding two fingers steady enough to permit a reliable reading while exercising is difficult. Accordingly, these systems also present unfavorable requirements necessary to properly enable the system.
Finally, a third class of heart rate monitors include those completely integrated within a wristwatch case but with the sensor integrated into the backside of the watch case. Measurements are made directly with the tissue in contact with the watch case. Typically, an optical source transmits infra-red light into tissue where it is modulated by flowing blood. The scattered light is received at a photodetector and converted to electronic impulses for analysis by a computer. These systems have a great advantage because they are completely self-contained and require no external supporting apparatus. However, they do suffer from measurement interruption due to poor coupling between the photodetector and tissue. Typically, the photodetector is quite small in size and cannot collect sufficient signal from the tissue. There is not much space between the detector and the tissue whereby a lens might be used to gather more light to improve the collection efficiency. In most cases, a detector of a few square millimeters is in direct contact with the tissue.
The following few paragraphs describe particular versions of these three cases and thus represents important related art.
Inventions relating to a measuring system which measures the function of the heart, including heart rate, from the user's body non-invasively includes a remote ‘functional unit’ which may be a transmitter attached particularly around the user's chest and a receiver unit worn on the wrist. Specifically, one might refer to the U.S. Pat. No. 6,183,422 of inventor Rytky where details of these systems will be found. These systems are highly functional and commercially available via the trade name ‘Polar’ among others. They do however have the disadvantage that the display is on the wrist while the sensor is disposed about the chest via a strap.
Kita in U.S. Pat. No. 5,650,945, also presents use of heart pulse sensor in communication via radio with a data processing system in a wristwatch reception unit. Communication between a remote sensing device and a display systems on a wrist offer users reliability but the inconvenience of requiring the chest strap mounted sensor which is not desirable.
One strategy embraced by inventor Pail of New York in U.S. Pat. No. 5,810,736, focuses on the notion that improved interaction cross-section can be achieved if the optical probe beam is made to interact with a region of increased blood flow. Pail forms his IR pulse rate system around the carpal tunnel region of the wrist where a higher density of blood is expected. In some versions, separate wrist bands support the sensor and display which may be spatially removed. In other versions, multiple optical detectors are used to increase the signal collected from the tissue. However, using multiple detectors increased the complexity, weight, and expense.
Heart rate monitors based upon near infra-red IR systems are presented in U.S. Pat. No. 5,853,372 issued on Dec. 29, 1998. These systems include a signal processing means which receives IR light from an optical detector coupled to living tissue. While these advanced systems employ sophisticated algorithms for processing return signals, they suffer because the signal collected from the tissue is weak and accompanied by significant noise. These systems suggest that picking up a strong return signal from the tissue will improve performance of detectors in IR based heart rate monitors.
Accomplished inventors Bryars and Cavanaugh, well known in the field, present another IR based system. In U.S. Pat. No. 5,807,267, electro-optic techniques are employed to form a heart rate monitor system. Again, special arrangements are provided to improve accuracy via signal processing. Specifically, a Fourier transform process serves to further separate the signal from the noise necessarily present in the signal produced in the tissue. This further illustrates the desire to efficiently collect sufficiently modulated signal from the test tissue. Where the signal is low, advanced methods of signal processing become required.
Bryars further teaches in U.S. Pat. No. 5,795,300 mounting means directed to improve sensor coupling and make it less susceptible to problems associated with body motion. Signals produced in-vivo are polluted with noise when a sensor is not particularly well coupled to tissue. The noise might have some characteristic which permits filtering. However, improvements to coupling also tend to reduce this problem.
Other systems of interest include those which provide heart rate measurement via optical technique but which do not include combination with a wristwatch system.
For example, inventor Sarussi presents a device suitable for heart rate monitoring via optical means in U.S. Pat. No. 6,553,242 issued on Apr. 22, 2003. The invention includes methods and devices for measurement of a level of at least one blood constituent. The device includes a light source and a light detector proximate the surface of an organ. The device and the method may be applied to monitoring, inter alia, conditions of apnea, respiratory stress, reduced blood flow in organ regions, heart rate, jaundice, and blood flow velocity.
Another invention taught by Khair and others in U.S. Pat. No. 6,533,729, includes a blood pressure sensor having a source of photo-radiation, such as an array of laser diodes. The sensor also includes a two-dimensional, flexible reflective surface which may be placed in contact with skin. The output from the array of photo-detectors is calibrated to blood pressure during a calibration procedure. The calibration relationship are then used during acquisition of blood pressure data to arrive at blood pressure data.
While systems and inventions of the art are designed to achieve particular goals and objectives, some of those being no less than remarkable, the are has limitations which prevent use of wrist worn heart rate monitors in new ways now possible. Inventions of the art are not used and cannot be used to realize the advantages and objectives of the inventions taught here following.